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Thanks for the info - bought the control amp but hesitated and decided to try freon with die to find any leak first. What do you know the High pressure hose next to the radiator was leaking really bad. It's easy to put Die in and really hard to change out the Amp so try the Die first and check the hose.  

I am so glad that I found this thread.  I have been having this same issue with my 2000 xterra for the last two summers.  It has been bothering me, but since it would eventually kick in the cold air about 10-20 down the road I just dealt with it.  Well, we finally bought new cars and I'm going to sell the xterra.  I wanted to fix the air before selling it, because I think that would just be wrong to sell it to someone the way it is.  I was afraid this was going to cost me $1,000 or more.  I just ordered the thermo amp and it is being shipping to me.  I will hopefully be able to switch it out this weekend.  I really hope this is the part that I need.  This is the first problem I've had with my xterra and it has over 140,000 miles on it.  I'm so thankful that this might not cost me any more than $50.00 and a little bit of time.  Thanks for all the information on this thread.  I may be back if this part doesn't fix anything.  

First, thanks for the installation guide for the TCA.  Changed that out, didn't fix the hot air.

Problem: Initially, intermittent cool, warm air. No clicking on/off of compressor like others had. Then, a week later, only hot air.  Also, hear hissing sound during this transition. Also, would hear air blowing out from near glove box, but that would go away.  Pressure in air flow was intermittently reduced at times.  Now, just warm/hot air coming out, no rapid on/off clicking, and good pressure flow.

Is this due to a leak somewhere?

Pressure hose?

Will I need to recharge?

Thanks in advance for any tips on this.

At least have experience changing TCA and knowing where to change out filters for cabin air.  

I have the same issues as everyone on here. Started with hissing come from the vents inside, refilled freon a couple times,now the intermittent hot & cold air with the compressor cycling on and off sporadically. Evacuated and refilled freon and still the same problem. Must have a small leak because it takes a year to get low on freon but now the issue of the Thermal Control Amp, I am going to get one and try it out, what do I have to lose!! Also, does the 2001 Frontier SE Crew Cab 3.3L V6 have cabin air filters?? This thread has been a real help!!  

I bought the Thermo Control Amp today and replaced it. It did not do the trick for me. My 2001 XTerra is having the "hiss" sound mentioned in previous posts. Getting to the sensor can be tricky, and I did not really see a good post on here regarding how to get to and replace the sensor. If you need to try and are stumped...give me a buzz @ 949.295.4002 and I am more than happy to walk you through it. nate  

The folks on this forum seem to have come to the same conclusion but if you're interested in reading more about the infamous TCA problem with Nissans (and it's not just the older models), it is well documented at http://www.nissanfrontier.org/forum_posts.asp?TID=2509&PN=1. This forum also includes a step-by-step set of photos someone generously posted showing how to get inside the compressor box and replace the TCA with no special tools. The TCA is about $40-$60 and can be replaced in about an hour or less.  

I have a 2000 Nissan Frontier 4x4 V6 3.3 liter, same mechanical as the X Terra. The AC has always been a problem. The high and low side hoses have been replaced 3 times each. When it was out of warranty I ordered the hoses on line and replaced them my self. Nissan wanted $400 for parts and labor on ONE hose. My 95 Nissan truck had the same hose problem. Save the old hoses and you can have a hose shop remake the hoses and save even more.  

I have a 2000 Nissan Frontier 4x4 V6 3.3 liter, same mechanical as the X Terra. My problem is the AC will not stay on. The high side is at 275 the low is at 25 at 95 degrees at about 15 percent humidity. The Nissan manual gives a range of 220-279 for the high side and 34-41 for the low side at 95 degrees.

The low side is to low and the high side is in the normal range. The Nissan manual gives the ambient air temps at 50-70% humidity. I live in Phoenix AZ and we hardly ever have that high of humidity.

Does anyone know what the adjustment to the range of pressures should be at a much lower humidity?

I have evacuated and charged it with the amount of Freon list on the sticker on the under side of the hood. It will cycle on and off at random. It seems to work fine in the garage with the gauges on it. But get it on the road and most of the time it will not work. I am thinking of replacing the themo control amp and see if that helps. The last time I took it to Nissan for another problem it was a pain; they stripped all the blots to the skid plate and did not fix the problem I had to take it back. I will avoid the dealer if possible.  

the pressure switch is on the liquid tank mounted in front of the condenser on my Frontier. It senses hi or low pressures and cuts off the compressor  

http://www.clubfrontier.org/forums/f23/frontier-service-manuals-available-download-46290/
the Nissan Frontier manuals are posted here, to my knowledge the X Terra is built on the same... what the word i am looking for.. frame and mechanical running gear as the Frontier.  

Well, I don't take my car to Nissan any more....
They cut off a heater hose on my car and used duct tape to fix it....I found this out because I went to another repair shop to get a second quote and five minutes after I dropped off my car they called me to tell me they wanted me to know that my heater hose is repaired with duct tape and they didn't want me to think they did it... They took pictures and sent them to me.  They were also kind enough to fix the hose with a clamp....
I went to Nissan and of couse they didn't do it.  I or my husband must have done this...well I'm don't know the first thing about car repairs and my husband the computer geek doesn't even know how to change oil...how the heck would we even know this hose was needing duct tape!!!!!!!!!
Find a reputable repair shop and stick with them, use the same machanic each time and you'll be happy.  

Wow! wish I'd done my research before flushing more $$ down the drain. I just returned from picking up my xterra '00 from Palm Springs, CA Nissan, and this time I refused to have them re-re-fix the A/c issue everyone's talked about. I Had the hoses replace 5/'08 $400.00 and now thats the same issue they're quoting for another $400.00 (different part# this time though). Intermitent A/C even after supposedly fixing it last time. Service Manager stated that their Nissan Master Technician (you be the judge on that), said it's only the hose, and that freon is low (same story as '08). Did I mention I've had it in since 2000 for every stated preventive maintenence schedule $1000's of $$. Dealership was sorry to lose me as a customer...but basically pay it or go elsewhere--Nice! After paying the $100.00 evaluation, I'm going elsewhere and now found these posts. Writing to Nissan as well, dealer owner, local media, blogs. In this economy you'd think customer service would rein supreme to keep great customers I'm driving Nissan's for 20+ years. These posts have been extremely helpful and thank you to everyone that's taken time to post and report these issues.bktonka  

please help!!!!

2000 Xterra and the a/c will not work has the common hissing problem but that does not even happen anymore.  I just replaced the thermo control amp and that didnt work.  I dont know what would be next.  The compressor never kicks on its like its broken.  If I didnt have any freon in the system could that cause the comp to never kick on?  Im thinking it could be one of the high pressure hoses.

Please any help would be great.  

I have a 2001 Frontier that had the same problem....sometimes the air would work fine all day, then in the evening the compressor would not engage at all. Andrew Nissan in Milwaukee said it was a compressor problem and replaced it (at my cost) but the problem presisted. Then an independent mechanic said it was the high pressure switch malfunctioning, so I had that replaced, but still the same problem. Sometimes the compressor would kick on and off very rapidly, but never stay engaged. Then, I came across this forum.......bought the $30 Thermal Amp....installed it myself..(And believe me, I am quite mechanically inclined and this was a real pain in the ass to do)and my problem is gone. Air has functioned fine ever since with no problems. It goes on when I want it to and off when I want it to. My only real regret is that I suffered for 2 years with this air conditioning problem and did not come across this forum sooner.

xtrudes.  

Thank you very much for this information. After spending $580 to have my a.c. repaired, it still wasn't working most of the time. I had the thermo control amplifier replaced and it works fine now. I just looked up my SUV at carfax.com and they mentioned this as a common problem with the 2000 Xterra. The part only cost $45 and I had it installed for $60. I wish I would have read your post before I had it repaired the first time.